myDATA — Greece's universal electronic books

myDATA (my Digital Accounting and Tax Application) is Greece's electronic-books platform, operated by AADE (Independent Authority for Public Revenue — the Greek tax authority). Since 2020-2021, every business must digitally transmit summaries of its income and expense invoices to AADE. It is a post-fact reporting model: the invoice circulates normally, then its data is reported — unlike clearance systems where the state validates the invoice before it is issued.

History — from A.1138/2020 to universal rollout

Greece had one of the EU's largest VAT gaps — the difference between VAT theoretically due and VAT actually collected. To close it, AADE designed a system where the administration no longer merely receives aggregated returns: it receives, almost continuously, a structured summary of every invoice. This is the logic of the "electronic books", formalised by joint decision A.1138/2020 of 12 June 2020, signed by the AADE Governor and the Ministry of Finance.

2018-2019  | AADE (the Independent Authority for Public Revenue) opens public
           | consultation on "electronic books". Goal: close the Greek VAT gap,
           | one of the highest in the EU (~25-30% at its peak).
           |
2020       | Joint decision A.1138/2020 (AADE + Ministry of Finance) of 12 June:
           | the legal framework for myDATA. Voluntary start, ramp-up planned for
           | autumn. COVID-19 shifts the timeline.
           |
2021       | 1 October: mandatory transmission of income (esoda) for every
           | business. Expenses (exoda) follow in tiers by turnover. Synchronised
           | with VAT returns.
           |
2022-2023  | Generalisation: classification (characterisation) of expenses,
           | automatic reconciliation e-books <-> VAT return, progressive
           | pre-filling. Penalties for non-transmission (A.1054/2021).
           |
2024       | myDATA <-> cash registers (FIM) and payment terminals (POS) linkage —
           | chaining transaction-collection-return. myDATA data is binding: the
           | VAT return must align.
           |
2025-2026  | myDATA becomes the bedrock of the B2B mandate (approved EU derogation)
           | and of ViDA alignment: the post-fact model evolves toward reporting
           | closer to real time via accredited providers.

Governance — AADE + Ministry of Finance

myDATA is operated by AADE (the Independent Authority for Public Revenue), made independent from the Ministry by Law 4389/2016. That institutional independence matters: it places the platform operator above political cycles, like an Anglo-Saxon revenue agency. The regulatory framework is set by A. decisions (Governor's decisions), each published in the Government Gazette (FEK).

The structuring texts: A.1138/2020 (myDATA framework), A.1054/2021 (procedures and penalties), and the later decisions that extend the set of transmission channels and the linkage to FIM cash registers. The technical specifications (XSD, API documentation) are published and updated on AADE's developer portal.

Technical schema — e-books, MARK, channels

Each business transmits an XML document (InvoicesDoc) summarising its invoices. AADE responds with a MARK (Monadikos Arithmos Katachorisis) — a unique registration number that seals the data in the electronic books, together with a verification QR code. The data feeds two books: the detailed book (analytiko) and the summary book (synoptiko) that reconciles with the VAT return.

• issuer / counterpart — issuer and customer AFM, country, branch.
• invoiceHeader — series, number (aa), date, myDATA invoiceType (1.1, 2.1, 5.1…), currency.
• invoiceDetails — lines: net value, vatCategory (1=24%, 2=13%, 3=6%…), income/expense classification.
• incomeClassification / expensesClassification — E3_* codes + category (core of the accounting characterisation).
• invoiceSummary — net, VAT, gross totals, broken down by classification category.

POST /myDATA/SendInvoices  (mydatapi.aade.gr/myDATA)
Headers:
  aade-user-id: TESTUSER
  Subscription-Key: <ocp-apim-subscription-key>
Content-Type: application/xml

<InvoicesDoc xmlns="http://www.aade.gr/myDATA/invoice/v1.0">
  <invoice>
    <issuer>
      <vatNumber>123456789</vatNumber>      <!-- issuer AFM -->
      <country>GR</country>
      <branch>0</branch>
    </issuer>
    <counterpart>
      <vatNumber>998877665</vatNumber>      <!-- customer AFM -->
      <country>GR</country>
      <branch>0</branch>
    </counterpart>
    <invoiceHeader>
      <series>A</series>
      <aa>4211</aa>                          <!-- number -->
      <issueDate>2026-06-16</issueDate>
      <invoiceType>1.1</invoiceType>         <!-- myDATA type -->
      <currency>EUR</currency>
    </invoiceHeader>
    <invoiceDetails>
      <lineNumber>1</lineNumber>
      <netValue>1000.00</netValue>
      <vatCategory>1</vatCategory>           <!-- 1 = VAT 24% -->
      <vatAmount>240.00</vatAmount>
      <incomeClassification>
        <classificationType>E3_561_001</classificationType>
        <classificationCategory>category1_1</classificationCategory>
        <amount>1000.00</amount>
      </incomeClassification>
    </invoiceDetails>
    <invoiceSummary>
      <totalNetValue>1000.00</totalNetValue>
      <totalVatAmount>240.00</totalVatAmount>
      <totalGrossValue>1240.00</totalGrossValue>
    </invoiceSummary>
  </invoice>
</InvoicesDoc>

<!-- AADE response: a MARK (unique registration number)
     plus a verification QR code -->

myDATA vs SdI vs KSeF — post-fact vs clearance

Three European CTC models, three philosophies. Italy (SdI) and Poland (KSeF) route the invoice through the state before it becomes valid. Greece lets the invoice circulate and captures its data afterwards:

Adoption — universal since 2021

• Mandatory income transmission since 1 October 2021 for nearly all Greek businesses required to keep accounts.
• Expenses (exoda) in tiers by turnover and accounting regime — generalised over 2022-2023.
• Automatic reconciliation e-books ↔ VAT return: since 2023-2024, the VAT return is pre-filled / checked against the electronic books.
• FIM + POS linkage: since 2024, fiscal cash registers and payment terminals feed myDATA, closing the transaction-collection-return loop on the B2C side.

Common pitfalls

• Thinking myDATA = e-invoicing. myDATA is primarily data reporting, not a mandatory B2B invoice format (that comes with the 2025-2026 B2B mandate). You can be myDATA-compliant while still sending a PDF to your customer.
• Forgetting classification (characterisation). An invoice transmitted without correct income/expense classification is incomplete: the E3_* codes must map to the line of the E3 tax form.
• e-books ↔ VAT desync. If the VAT return differs from the electronic books, AADE detects it automatically — a discrepancy to justify, audit likely.
• Wrong invoiceType. myDATA types (1.1 sale of goods, 2.1 services, 5.1 credit note…) are not interchangeable: the wrong type skews classification and aggregates.
• Ignoring the MARK. Without archiving the returned MARK, you cannot prove transmission in an audit. The MARK is the proof, not the invoice itself.

Cross-links

• Greece hub — full view
• myDATA — classification and characterisation
• B2B mandate 2025-2026
• Accredited provider model
• VAT (FPA) regimes
• myDATA and ViDA 2030
• AADE — official myDATA portal
• AADE — e-books documentation